A coin return mechanism of this type is described for example in European patent application EP-1020818-A1, which is a return in which different denominations of coins can be mixed, having the particularity that the coins are identified in a step prior to the extraction, being able to decide if said coins should be extracted or not, according to their values.
This type of device has the advantage that a single return replaces two or more mechanisms of the single coin type with the savings of space and costs this implies. Nevertheless, they have the consistent drawback that, as one type of coins are limited in the storage area or hopper, the return times for this coin in particular can be excessively longer, even rendering the machine in which it is assembled out of service.
The same occurs if the distribution of coins inside the hopper is not homogenous, for example if the coins that are to be extracted are at a certain time accumulated far from the extractor disk, the same effect as that previously mentioned will occur.
Processes have been developed which try to reduce as much as possible the problems resulting from the limitation of coins in other types of return systems, for example those based on several vertical pipes, each of them storing a single type of coin. The publications of European patents EP-0653085-B1 an EP-0841645-A2 can be mentioned as documents of interest. These documents describe processes to optimize the number of coins of the return system to prevent as much as possible that the machine in which the coin system is installed is put out of service or working under the condition of exact change when any of the coins required for returning the excess credit introduced by the user have run out. One of the described processes consists of calculating the possible combinations of coins that add up to the credit to be returned and choosing the one using the lesser amount of coins, and another process further takes into consideration other conditions to change the initially chosen combination for another one which, even though it is not the optimal combination of the minimum number of coins, maintains the stock of a certain type of coin which would run out if the first process would be used. These types of processes can be carried out in the return systems in which there is only one type of coin per storage area, and the number of coins of each of the storage areas/returns, such that it is known beforehand the status of each of the returns before and after the return process, and the extraction of coins of which there are available units in the returns can furthermore be assured.